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N. Nicodemus, J.García, R. Carabaño and C. de Blas
Departamento de Producción Animal, ETSI Agrónomos
Universidad Politécnica de Madrid
28040, Madrid, SPAIN
Commercial rabbit diets usually contain around 32-38% of NDF. Fibre is required in
these diets to regulate rate of passage, to control gut flora and to maintain integrity of
intestinal mucose (De Blas et al., 1998). Furthermore, fibre particle size has a large influence
on fibre digestion (Laplace and Lebas, 1977; Gidenne, 1993; García et al., 1996). Recently,
Nicodemus et al. (1997) have established that a minimal proportion of a 21% of large
particles (> 0.315 mm) is needed to get maximal performance in rabbits.
Soybean hulls (SBH) is a low lignified (around 3% ADL on DM) source of fibre, so
that its inclusion in commercial diets usually leads to a decrease of dietary lignin
concentration. Degree of lignification of the cell wall has been reported as a main negative
factor on fibre digestion efficiency (Gidenne and Perez, 1994; García et al., 1996). Part of this
effect might be explained by a parallel negative influence on caecal mean retention and
fermentation time (Gidenne and Perez, 1994). Furthermore, semisynthetic diets containing
purified lignin as source of fibre led to an increase of intestinal mucose damage with respect
to diets based on cellulose or pectin (Chiou et al., 1994). Other studies (Motta et al., 1996;
Carabaño et al., 1997) showed that an increase in the degree of lignification decreased caecal
VFA concentration and increased caecal pH, which might favour proliferation of pathogenic
flora (Prohaszka, 1980). Otherwise, a faster rate of passage of high lignified diets might be
associated to a higher DM intake, as observed by Perez et al. (1994) in fattening rabbits. From
these results, it can be derived that an optimal lignin concentration might be required for
maximal performance of highly productive rabbits. However, in most of these studies,
changes in dietary lignin concentration were parallel to variations of total fibre content and
feed particle size, which makes difficult the identification of the effects.
The aim of this work was to measure the digestion efficiency and performance
response of highly productive does and growing rabbits to an increase of level of inclusion of
SBH and a parallel decrease in dietary lignin content. Four isofibrous diets of similar particle
size were used, with level of inclusion of SBH and acid detergent lignin concentration ranging
from 0 to 400 g/kg and from 59 to 33 g/kg DM, respectively.
Four (A to D) isofibrous (around 430 g/kg NDF on DM) diets containing 0, 133, 266
and 400 g/kg of SBH and 59, 50, 41 and 33 g ADL/kg DM were made. They were formulated
to meet or exceed all the essential nutrient requirements of a mixed feed for lactating and
growing rabbits (Lebas, 1987), by gradual substitution of a mixture 50:50 of alfalfa hay and
wheat straw by soya bean hulls. Diets had a similar particle size distribution and at least a
21% of large particles (> 0.315 mm). The ingredient and chemical composition of the
experimental diets are shown in Tables 1 and 2, respectively.
Digestibility Trial
A group of 40 New Zealand x Californian growing rabbits (ten per diet) from 60 to 70
days of age, weighing 2.11 ± 0.05 kg as average, was alloted at random to the four
experimental diets to determine the apparent digestibility of DM, energy, CP and NDF. No
control of sex or litter was done. Following a 30-d period of adaptation to each diet, the feed
intake (ad libitum access) and the total faecal output (caecotrophy was not prevented) were
recorded for each rabbit over a 4-d period.
During all the trials, rabbits were housed in a building in which the temperature was
partially controlled (average room temperature 20 ± 3ºC). Animals were handled according to
the principles for the care of animals in experimentation published by the Spanish Royal
Decree 223/88. A cycle of 12 h of light and 12 h of dark was used throughout this trial.
Caecal Digestion Trial
Seven days after the digestibility trial, animals were slaughtered (average weight 2.2 ±
0.06) by cervical dislocation one hour before dark (around 19:00 h) to avoid the period of soft
faeces excretion. The stomach and caecum were weighed separately with and without their
contents. Caecal pH was immediately measured and caecal content was centrifuged at 25000
g at 0ºC for 10 min. The supernatant fluid was used to determine ammonia and VFA
concentrations. A solution of 5% orthophosphoric acid (v/v) plus 1% mercury chloride (w/v)
was added (0.1 ml/ml) to the samples for VFA determination. Samples for ammonia
determination were acidified with a solution 0.2 M hydrochloric acid (1 ml/ml).
Growth Trial
One hundred and sixty New Zealand x Californian weanling rabbits (forty per diet)
were blocked by litter and assigned to the treatments. No control of sex was done. After
weaning, rabbits were individually caged and had ad libitum access to the feed, until they
reached approximately 2 kg of body weight. Feed intake and length of the experimental
period were recorded per cage.
Lactation Trial
Forty-eight New Zealand x Californian doe rabbits (12 per diet) were assigned at
random to the experimental diets. A 60-d adaptation period was allowed before recording
rabbit performance. Remating interval after parturition was fixed at 7 days and weaning age at
30 days. The experimental diets were offered ad libitum in late pregnancy (from day 28 on)
and throughout lactation. Weight of does was determined at the beginning and at the end of
the lactation period. Does were separated from their litters after parturition. Milk production
was estimated daily from weight loss of does during suckling. Feed intake of does was
determined separately from that of young rabbits every 10 days. Growth and feed intake of
young rabbits from 21 days of age until weaning was measured.
Animals were housed in flat-deck cages measuring 600 x 500 x 330 mm high. A cycle
of 16 h light and 8 h dark was used throughout the experiment. Building heating systems and
forced ventilation allowed the temperature to be maintained at 21 ± 4ºC.
Analytical Methods
Chemical analysis of diets and faeces was made using the method of Van Soest et al.
(1991) for NDF, and Goehring and Van Soest (1970) for ADF, ADL and acid detergent cutin
(ADC). Neutral detergent fibre was determined directly, whereas ADF and ADL were
extracted successively. Acid detergent cutin was determined after extracting ADF, ADL and
permanganate lignin. Procedures of the Association of Official Analytical Chemists (1990)
were used for dry matter, ash and crude protein. Gross energy was determined by adiabatic
bomb calorimetry.
Caecal ammonia was analysed using the autoevaluation distillation unit Kilab
nitrolab-auto. Samples were distilled with a solution of sodium tetraborate (2.5%) collected
on boric acid solution (1%) and valorised with hydrochloric acid (0.05 M) and a colour
indicator. Caecal VFA concentration was determined in a Hewlett-Packard (5710 A) gas
cromatograph, with a flame ionization detector, a Hewlett-Packard (3390 A) recorder
integrator and a steel column (FFAP 10% H3PO4; 1% WAW, 100 to 120 mesh). The carrier
gas was nitrogen with a flow rate of 30 ml/min. Hydrogen and air flows to the detector were
30 and 200 ml/min. Injector and detector temperatures were 250ºC. The oven temperature
was increased during the analysis from 110 to 160ºC at a rate of 80ºC/min.
Distribution of particle size of diets was determined on two samples of pellets by wet
sieving. A dried sample of 55 g was placed in 1100 ml of distilled water and 30 ml of
commercial detergent. It was left overnight stirring at room temperature. Then it was emptied
onto a sieve stack with four sieves with decreasing pore sizes: 1.25, 0.635, 0.315 and 0.160
mm, and washed with water for 20 min. The 1.25-mm sieve was then removed, allowed to
drain for 1 h and weighed. The same process was done during 10, 6 and 4 min for the sieves
with pore sizes 0.635, 0.315 and 160 mm, respectively. The flow of water used was 1.5-2
l/min. After that, all the samples collected were transferred to different trays and DM was
determined. Particle size of the experimental diets is shown in Table 2.
Statistical Analysis
Data were analysed by using the GLM procedure of SAS (1990). Treatment sums of
squares were partitioned into linear and quadratic effects. Mean comparisons were made
using orthogonal contrasts. Data from caecal digestion and growth trials were analysed as a
completely randomized block design with litter as block effect and type of diet as the main
source of variation. Weaning and slaughter weights were used as linear covariates in the
growth and caecal digestion trial, respectively. Lactation trial was analysed as a randomized
complete design with type of diet as the main source of variation. Day of effective mating and
litter size at weaning were used as linear covariates. Interactions between type of diet and day
of lactation were studied using a repeated measures analysis (SAS, 1990). All data are
presented as least square means.
Digestibility Trial
The effect of dietary treatment on nutrient digestibility is shown in Table 3. Feed
intake tended to be lower (P = 0.06) in animals fed the highest SBH level (diet D, 139 g/d)
with respect to the average of the other three diets (157 g/d). An increase of SBH level or a
decrease of dietary ADL content led to a linear increase of NDF, energy and DM
digestibilities by 28, 4 and 4% between the extreme diets (P = 0.004, 0.06 and 0.02,
respectively) and to a linear decrease of CP digestibility (P < 0.001).
Caecal DigestionTrial
Feed intake tended also to be lower in this trial (Table 4) for diet D than for the other
diets (134 vs 169 g/d; P = 0.07). Treatments had no effect on weight of stomach, but weight
of stomach contents decreased linearly (from 31.9 in diet A to 25.5 g/kg BW in diet D; P =
0.01) when level of inclusion of SBH increased. Weights of caecum and caecal contents were
higher, and caecal pH lower (P = 0.009, 0.02 and 0.009, respectively) for rabbits fed the diet
with the highest SBH level (400 g/kg) than for those receiving diets containing from 0 to 266
g SBH/kg (1.99 vs 1.68, 5.13 vs 4.48 and 5.80 vs 5.96, as average, respectively). Caecal
ammonia concentration was not affected by treatment.
An increase of SBH level of inclusion or a decrease of dietary ADL concentration
increased linearly (P = 0.05) total VFA concentration by 22% between extreme diets. Type of
diet did not affect molar proportion of acetic acid, but those of propionic and butiric acid
respectively increased (from 48.9 to 63.4) and decreased (from 217 to 179 mmol/mol VFA)
linearly (P = 0.04) when level of SBH increased from 0 to 400 g/kg.
Growth Trial
The effect of diet on growth traits is shown in Table 5. Average daily gain was lower
for rabbits fed the diet with the highest level of SBH with respect to the other three diets, both
in the two first weeks after weaning (44.4 vs 46.5 g/d; P = 0.02) and in the whole fattening
period (40.2 vs 42.2 g/d; P = 0.04). A parallel effect was observed on feed intake, which
decreased (P < 0.001) from 93.8 (as average of diets A, B and C) to 82.9 g/d for diet D in the
two first weeks, and from 123 to 110 g/d in the whole fattening period. Contrasts between diet
C and the average of diets A and B or between diets A and B were not significant for these
On the contrary, feed efficiency (expressed as g of weight gain per g of feed intake)
was higher in the whole fattening period (P = 0.03) for the diet with the highest SBH level
(0.360) than for average of the other three diets (0.343). This difference was more significant
(P < 0.001) and quantitatively higher (8%) in the two first weeks after weaning period.
Lactation Trial
Type of diet affected daily feed intake, total milk production, maximal daily milk
production and litter weight at 21 days (Table 6). These traits were higher (P < 0.001) for the
diet containing 0 g SBH/kg and 59 g ADL/kg DM (413 g, 6.17 kg, 316 g and 3.11 kg) than
for the average of the other diets (372 g, 5.41 kg, 284 g and 2.83 kg, respectively). No
significant differences among diets were found beyond this level.
Treatments had no effect either on weight gain of rabbit does during the period of
lactation, or on dry feed intake and weight gain of young rabbits from 21 to 30 days of age.
As a consequence, litter weight at weaning followed a similar trend than at 21 days of age, but
differences among diets did not reach a significant level (P > 0.05). Feed efficiency
(expressed as kg of rabbit weaned per kg of feed intake) tended to increase slightly and
linearly (P = 0.03) when increasing SBH inclusion level. No interaction was found between
type of diet and period of lactation on any of the traits studied.
An increase of level of inclusion of SBH from 0 to 400 g/kg in parallel to a decrease
of dietary ADL concentration from 59 to 33 g/kg DM, resulted in a linear increase of NDF
digestibility (NDFd) from 0.21 to 0.27. These results agree with those reported by Gidenne
and Perez (1994) when altering the proportion of five fibrous ingredients in five experimental
diets and by García et al. (1996) when comparing six semisynthetic diets containing different
fibrous by-products. As in other species, lignin may difficult digestion in rabbits through its
covalent linkages with other cell wall components (Van Soest, 1994). Furthermore, Gidenne
and Perez (1994) observed a negative effect of dietary lignin on total and caecal retention
time. This would limit fibre digestion, as caecum is the main fermentative area in rabbits.
On the other hand, an increase of SBH level led to a linear decrease of CP
digestibility. This result could be related to the lower digestion efficiency of protein in soya
bean hulls (0.31; García et al., 1998) with respect to that of alfalfa hay (0.72 as average,
García et al., 1995). This effect compensated partially the increase in NDFd, so that variations
in energy and DM digestibilities were parallel to that of NDFd, but its extension and
signification were lower.
This experiment indicates that a maximal level of inclusion of SBH of 266 g/kg is
recommended or a minimal ADL concentration of 41 g/kg DM (diet C) is required in
fattening feeds to achieve a maximal feed intake and daily gain. These traits decreased by 10
and 5%, respectively, in rabbits fed the diet containing 400 g SBH/kg or 33 g ADL/kg DM
(diet D), with respect to the average of the other three diets. These results agree with those of
Perez et al. (1994) who reported a decrease of average daily gain when dietary ADL content
decreased from 40 to 20 g/kg.
A similar, but negative, effect of treatments was observed on weight of caecal
contents, which was 14% higher for diet D than for the average of diets A to C. These
results agree with the negative influence of dietary lignin on weight of the caecal contents
observed by De Blas et al. (1998) when reviewing data from forty experimental diets. This
relationship might be explained by a parallel effect of dietary lignin on caecal retention
time, as observed by Gidenne and Perez (1994), that in our study would be independent of
feed particle size.
Altogether, these results seem to indicate that accumulation of digesta in the
caecum might have a negative effect on feed intake capability, in a similar way as rumen
fill has in ruminants (Van Soest, 1994). Previous work by García et al. (1993) has also
shown that inclusion of sugar beet pulp in fattening diets led both to a decrease of feed
intake and weight gain and to an increase of caecal contents weight.
Type of diet had an opposite effect on stomach than on caecal contents weight.
Accordingly, it should not be expected an important effect of treatments on carcass
dressing performance (not measured in our study).
An increase of level of inclusion of SBH or a decrease of dietary ADL
concentration led to a linear increase of caecal VFA concentration and to a decrease of
caecal pH. These effects might be related to the parallel increase observed of NDFd, as
fibre is a main energy substrate for caecal flora. Furthermore, phenolic groups in lignin
have buffer exchange properties (Van Soest, 1994). Accordingly, it should be expected a
decrease of cation exchange capacity of caecal contents (not measured in our study) when
decreasing ADL level, which would favour a decrease of caecal pH. The effect of diet on
these traits could explain a negative effect of dietary lignin on enteritis incidence. In this
way, several authors (Sakata, 1987; Gardiner et al., 1995) have related an increase of
hindgut VFA concentration to an improvement of mucose integrity. This effect might be
explained since VFA are used by the colonocytes as the main energy source (Vernay,
1987). Furthermore, Prohaszka (1980) and Wallace et al. (1989) have reported a negative
effect of acidity and VFA concentration on in vitro proliferation of Escherichia coli.
However, Perez et al. (1994) using a large number of animals (409 per diet), observed a
trend (P = 0.06) for a linear increase of mortality in fattening rabbits when dietary ADL
content decreased from 76 to 20 g/kg. These authors have hypothesised that the favourable
effect of lignin found in their study on fattening mortality could be related to its positive
effect on rate of passage of feed. The results of our study did not show a significant effect
of type of diet on fattening mortality, probably because of the lower number of rabbits
involved. However, it tended (P = 0.15) to be higher in the diet with the highest SBH level
(400 g/kg), with respect to the average of the other three diets, in accordance with the
previous results.
A minimal ADL content of 59 g/kg DM was required to maximise feed intake of
lactating does, milk production and litter weight at 21 days, according to the results of our
study. However, the effect of type of diet on litter weight at weaning was less significant,
as no differences in dry feed intake by young rabbits were found.
These results might indicate a higher lignin requirement for maximal performance
in lactating than in fattening rabbits. They agree with the higher total NDF requirements
observed for lactating does (35.5% on DM, De Blas et al., 1995) with respect to growing
rabbits (28.1%, De Blas et al., 1986). However, practical recommendations for minimal
fibre content (e.g. Lebas, 1987) are usually higher for adult than for fattening diets,
probably because of the need of preventing the higher diarrhoea incidence in the latter.
These higher lignin and fibre requirements of lactating does might be related to its
higher energy requirements and feed intake per unit of body weight with respect to
growing rabbits. Both dietary lignin and fibre levels are major enhancing factors of rate of
passage and then of intake capability (Van Soest, 1994). Caecal traits were not measured in
adult does in our study. Our results suggest that pattern of caecal transit time and caecal
contents turnover might differ in lactating does from those of growing rabbits for a given
diet. In fact, previous work (De Blas et al., 1995) has shown an interaction between age
and type of diet on fibre digestibility.
An increase of SBH level or a decrease of dietary ADL content increased slightly
and linearly feed efficiency. Differences between extreme diets were 6 and 9.5% in
fattening and lactating rabbits, respectively. Similar effects have been observed by Perez et
al. (1994) in growing rabbits. This result might indicate that the decrease of animal
performance at low lignin levels was compensated by an increase in nutrient digestion
efficiency. However, the difference between extreme diets in energy digestibility in our
study was only a 3%, which suggests further effects of type of diet. In this way, high
dietary ADL contents might lead to a decrease of fat content in live weight gain (not
measured in our study). Furthermore, the negative effects of dietary lignin on energy
digestibility might be enhanced in adult does with respect to younger animals.
1.- An increase of level of inclusion of SBH from 0 to 400 g/kg, in parallel to a decrease
of dietary ADL concentration from 59 to 33 g/kg DM, led to a linear increase of NDF and
energy digestibilities and feed efficiency in fattening and lactating rabbits. The differences
between extreme diets for these traits were 28, 4, 6 and 9.5%, respectively.
2.- Weights of caecum and caecal contents were higher and caecal pH lower (by 18, 15 and
3%, respectively) for the diet with the highest level of inclusion of SBH (400 g/kg) than for
the average of the other three diets. An increase of SBH level of inclusion from 0 to 400
g/kg or a decrease of dietary ADL content from 59 to 33 g/kg DM increased linearly caecal
VFA concentration (by 22%) and molar proportion of propionic acid (by 30%) and
decreased that of butiric acid (by 21%). Type of diet did not affect either molar proportion
of acetic acid or caecal ammonia concentration.
3.- Feed intake and performance of growing and lactating rabbits were maximal for ADL
concentrations of 41 and 59 g/kg DM, respectively. Average daily gain, milk production
and feed intake were impaired by 5, 14 and 12%, respectively, in animals fed diets
containing under optimal ADL contents.
4.- These results show a high performance and efficiency of fattening feeds containing a
26.6% of SBH, a level much higher than those used at present in such diets in Spain
(maximum 10%, according to FEDNA, 1997).
5.- Inclusion of SBH had negative effects on milk production, although positive on feed
efficiency in lactating does. Our results indicate that lignin requirements for maximal
performance are higher for lactating than for growing rabbits. This enhances the interest of
combining the use of SBH with that of inexpensive highly lignified by-products (as wheat
straw or grape seed meal) in diets for rabbit does.
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Table 1
Ingredient composition of experimental diets
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL content (g/kg DM) 59 50 41 33
Ingredient, g/kg
Alfalfa hay 200 133 66 0
Wheat straw 200 133 66 0
Soya bean hulls 0 133 266 400
Barley grain 76 76 76 76
Cane molasses 10 10 10 10
Pork lard 21 21 21 21
Sunflower meal 147 147 147 147
Full fat soybean 70 70 70 70
Corn gluten feed 49 49 49 49
Wheat bran 200 200 200 200
Calcium carbonate 9.7 9.7 9.7 9.7
Dicalcium phosphate 9.7 9.7 9.7 9.7
Sodium chloride 4.8 4.8 4.8 4.8
Robenidine premix a 1 1 1 1
Alimet 0.4 0.4 0.4 0.4
Choline chloride 0.3 0.3 0.3 0.3
Vitamin/mineral premix b 1.6 1.6 1.6 1.6
a 66 g/kg of active ingredient Supplied by Impex Ibérica, SA
b Provided by Roche Vitaminas, SA. Mineral and vitamin composition (g/kg): Mn, 13.4; Zn, 40; I, 0.7; Fe, 24; Cu, 4;
Co, 0.35; riboflavin, 2.1; calcium pantothenate, 7.3; nicotinic acid, 18.7; menadione, 0.65; α-tocopherol, 17; thiamin,
0.67; pyridoxine, 0.46; biotin, 0.04; folic acid, 0.1; cyanocobalamin, 7 mg/kg; vitamin A, 6700,000 IU/kg; vitamin
D3, 940,000 IU/kg.
Table 2
Chemical composition an particle size of experimental diets (g/kg DM)
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL content (g/kg DM) 59 50 41 33
Chemical analysis
DM 914 911 919 909
Ash 96 92 89 83
CP 197 176 180 184
NDF 425 437 438 431
ADF 250 257 261 264
ADL 59 50 41 33
Acid detergent cutin 27 29 23 20
Gross energy (MJ) 19.0 18.9 18.8 18.6
Particle size
> 0.160 mm 377 373 389 421
> 0.315 mm 287 289 302 329
> 0.635 mm 167 181 191 184
> 1.25 mm 33 33 41 43
Table 3
Effect of type of diet on apparent nutrient digestibility
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL content (g/kg DM) 59 50 41 33 SEM(1)
Feed intake, g DM/d 155 159 156 139 8.0
Digestibility coefficients
DM 0.537 0.547 0.534 0.565 0.007
Energy 0.550 0.563 0.547 0.575 0.007
NDF 0.209 0.246 0.229 0.271 0.012
CP 0.766 0.734 0.722 0.712 0.007
1 n = 10
Table 4
Effect of type of diet on caecal traits
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL content (g/kg DM) 59 50 41 33 SEM1
Feed intake, g DM/d 160 172 174 134 9.6
Stomach weight (g/kg BW) 11.0 10.9 11.0 10.4 0.5
Stomach content weight (g/kg BW) 31.9 30.2 25.0 25.5 2.1
Caecal weight (g/kg BW) 16.0 18.2 16.4 19.9 0.9
Caecal content weight (g/kg BW) 42.9 46.0 45.7 51.3 2.2
Caecal pH 5.99 5.97 5.92 5.80 0.05
Ammonia concentration (mmol N-NH3/l) 12.8 9.60 10.7 11.8 1.58
Total VFA (mmol/l) 59.6 65.4 70.8 72.6 4.86
Molar proportions (mmol/mol VFA)
Acetic acid 734 738 758 757 13
Propionic acid 48.9 57.5 53.6 63.4 36
Butiric acid 217 204 188 179 120
1 n = 10
Table 5
Effect of type of diet on fattening performance
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL concentration (g/kg
DM) 59 50 41 33 SEM1
Two weeks after weaning period
Average daily gain (g) 47.2 45.1 47.1 44.4 0.72
Feed intake (g/d) 97.0 93.2 91.1 82.9 1.55
Feed efficiency (g gain/g intake) 0.49 0.49 0.52 0.54 0.008
Whole fattening period
Average daily gain (g) 42.3 41.4 43.0 40.2 0.78
Feed intake (g/d) 122 123 123 110 1.81
Feed efficiency (g gain/g intake) 0.34 0.34 0.35 0.36 0.005
Mortality (%) 6.66 10.0 6.66 17.2 5.53
1 n = 40
Table 6
Effect of type of diet on rabbit does performance
Level of inclusion of SBH (g/kg) 0 133 266 400
Dietary ADL content (g/kg DM) 59 50 41 33 SEM1
Feed intake of rabbits does (g/d) 413 385 378 353 8.97
Milk production per lactation (kg) 6.17 5.48 5.42 5.33 0.19
Maximal daily milk production (g) 316 286 291 276 9.36
Day of lactation of maximal milk production 16.4 17.4 17.3 17.6 0.77
Dry feed intake of young rabbits 21-30 days (g/d) 155 159 117 149 14.0
Average daily gain of young rabbits 21-30 days (g) 25.4 23.9 24.8 25.8 1.31
Litter weight at 21 days of age (kg) 3.11 2.86 2.82 2.80 0.09
Litter weight at weaning (kg) 5.17 4.85 4.86 4.93 0.17
Feed efficiency (kg weaned/kg feed) 0.42 0.42 0.43 0.46 0.014
1 n = 12
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Title GB: Dietary lignins in growing rabbits. 1- Consequences on digestibility and rate of passage.
Four rabbit diets were formulated to study the effect of a progressive inclusion (0, 100, 200, and 300 g kg − 1) of sugarbeet pulp (SBP) substitute for alfalfa hay (AH). The control diet contained 500g kg−1 of AH and 190 g kg−1 acid detergent fibre (ADF) on a DM basis. In Experiment 1, 32 Californian x New Zealand White rabbits were used to determine dietary nutrient digestibility. The inclusion of SBP quadratically increased (P < 0.01) digestibility coefficients of NDF, ADF and gross energy, showing a maximum for the diet containing 200g kg−1 of SBP. Crude protein digestibility linearly increased with SBP inclusion (P < 0.05). In Experiment 2, 36 rabbits fed the same diets as in Experiment 1 were used to determine several digestive traits and the efficiency of utilization of dietary energy for growth. Dietary inclusion of SBP did not affect either the concentrations of ammonia (66 mg of N-NH3 per litre) and total VFA (50.3 mmol l−1) or the molar proportion of VFA (767, 62 and 171 mmol mol−1 VFA of acetate, propionate and butyrate, respectively) in the cecal digesta. The concentration of starch in the ileal digesta was also unaffected by diet (7.7 g kg−1 of DM, as average). The weight of cecal contents increased (P < 0.05) and the pH of cecal contents decreased (P < 0.05) when SBP proportion in the diet increased. The efficiency of utilization of dietary digestible energy for growth was not influenced by dietary SBP inclusion (0.224, as average).
Rate of passage measurements (RPM) of different cell wall (CW) particle sizes (0.05 mm < S1 < 0.315 mm, 0.315 mm < S2 < 0.5 mm, 0.5 mm < S3 < 1 mm, S4 > 1 mm) were investigated in two groups of four adult rabbits fed on two diets differing in their level of lignocellulose (acid detergent fibre, ADF): control (C) = 16.0% ADF; high (H) = 21.8% ADF. In order to determine the specific effect of fibre level without an effect on intake, the diets were given in the same quantities (110 g day−1). CW particles of each size class (S1–S4) were labelled with 141Ce. RPM were performed by following the faecal excretion of 141Ce for 6 days.The total mean retention time (TMRT) of CW was slightly reduced when the level of ADF increased (under similar feed intake level), being 30.2 h and 28.8 h for C and H groups, respectively. The retention time in the mixing compartment (RTM) or in the ‘terminal component’ (TCRT) was not affected by dietary ADF level (mean values of 23.4 h and 26.8 h, respectively).The higher TMRT of fine particles (32.2–36.6 h for S1) compared with that of larger particles (25–29 h for S2–S4) were related to the anti-peristaltic activity of the proximal colon. Particles between 0.3 and 1 mm in size did not show any differential rate of passage. That the transit time (TT) did not differ (mean of 7.0 h) between particle classes suggested that no particle segregation (between S1 and S4) occurred in the small intestine and distal colon of the rabbit. In contrast, RTM increased from 20.6 h for S1 to 26.2 h for S4.
Fifty-one New Zealand White × California rabbits were used to evaluate apparent in vivo dry matter (DM), organic matter (OM), energy, nitrogen (N), neutral detergent fibre (NDF) and amino acid digestibilities of five lucerne hays varying in chemical composition. Hays were ground and pelleted and given as sole feeds throughout the experiment. In vitro DM, OM, NDF and N digestibilities of feed samples were also determined. A ruminal incubation trial was performed to determine NDF disappearance of lucerne hays in nylon bags. The type of lucerne hay had a large effect on its nutritive value. The range of variation for digestible energy (DE) and digestible crude protein (CP) contents and for NDF digestibility was 6.4–9.2 kJ g−1, 114–164 g kg−1 and 0.204–0.276, respectively. The type of lucerne hay also affected lysine, methionine and threonine digestibilities. Stepwise regression analysis showed that the best single predictors for energy, CP, NDF and amino acid digestibilities were dietary NDF and non starch polysaccharide (NSP) contents, ruminal NDF degradability after 48 h of incubation and CP digestibility, respectively. Regressions using only chemical components as independent variables were also calculated. The results of this study showed that in vitro methods and prediction equations determined for mixed diets and concentrated ingredients need to be adjusted to estimate nutritive value of forages in rabbits.
Four diets were formulated to study the effect of a progressive substitution of grape pomace (GP) for alfalfa hay (AH) at the rates 0, 100, 200 and 300 g/kg total weight. The control diet contained 500 g AH and 192 g acid-detergent fibre per kg dry matter (DM). In experiment 1, 32 Californian × New Zealand White rabbits were used to determine dietary nutrient apparent digestibility. The inclusion of GP decreased the apparent digestibility of crude protein (P < 0·001) and energy (P < 0·05). However, the digestible energy (DE) contents of the diets were similar because GP had a greater gross energy content than AH. In experiment 2, 36 rabbits given the same diets as in experiment 1 were used to determine several digestive and productive traits and chemical body composition (at 20kg live weight). Dietary inclusion of GP linearly decreased ammonia (P < 0·01), total volatile fatty acid concentration (P < 0·001) and the molar proportion of acetate (P < 0·05) in the caecum. Starch content in the Heal and caecal contents was low but linearly increased (P < 0·05) with increasing dietary concentration of GP. The average daily gain (from weaning at 30 days of age to 2·0 kg live weight) was not significantly affected (P > 0·10) by the diet, but the ratio gain: food linearly decreased (P < 0·001) with the GP inclusion. Dietary inclusion of GP linearly increased (P < 0·10) the fat content of the empty body of the rabbits. The efficiency of utilization of dietary DE and protein for growth were calculated by the comparative slaughter method, using the chemical body composition data of 22 suckling rabbits slaughtered at 30 days of age for the initial body composition. The efficiency of utilization of DE was not influenced by dietary GP inclusion, but GP linearly increased (P < 0·01) digestible crude protein utilization. The decrease in crude protein apparent digestibility may be the main reason that gain: food ratio was impaired in diets containing GP substituted for AH.
Attempts were made to establishEscherichia coli ML308 in the sheep rumen by inoculating it in combination with the slowly metabolized sugar alcohol, sorbitol. Numbers were determined by plating dilutions on nutrient agar containing the chromogenic -galactoside, 5-bromo-4-chloro-3-indolyl--d-galactoside. This strain, alac-constitutive mutant, produced distinctive blue colonies.E. coli ML308 failed to grow in rumen fluid, despite being able to grow rapidly on sorbitol and in rumen fluid at pH 7.0. Its growth rate was depressed by relatively small drops in pH in the presence of volatile fatty acids (VFA), such that normal pH's of 6.2–6.6 in rumen contents were inhibitory. The indigenous remen bacterium,Streptococcus bovis, was much more resistant to the combination of high VFA concentrations and low pH. The success of this and similar strategies for the introduction of new organisms with beneficial new properties will, therefore, depend on the organism's having a tolerance to VFA over a range of rumen pH that enables them to survive in the same way as native species.